1. Field of the Invention
The present invention relates to an ultrasonic imaging method and an ultrasonic imaging apparatus for performing diagnosis on internal organs in a living body or nondestructive inspection by using ultrasonic waves.
2. Description of a Related Art
Generally, in an ultrasonic imaging apparatus including an ultrasonic diagnosing apparatus, an industrial defect detecting apparatus, etc., an ultrasonic transducer array including plural ultrasonic transducers having functions of transmitting and receiving ultrasonic waves is used. In the ultrasonic imaging apparatus having the ultrasonic transducer array, image information on an object to be inspected is obtained by scanning the object with a sound beam formed by synthesizing plural ultrasonic waves. Then, a two-dimensional or three-dimensional image on the object is reproduced based on this image information.
In such ultrasonic imaging apparatus, as a method of transmitting and receiving ultrasonic beams by using an ultrasonic transducer array, the following systems (1) and (2) are known. In addition, designing of ultrasonic beams is described in Hiroshi Kanda et al., “DIGITAL ULTRASONIC TECHNOLOGY”, Extra Number of Clinical Radiation, KANEHARA & CO., JP, 1998, Vol. 43, No. 11, pp. 1248-1252.
(1) Unidirectional Ultrasonic Beam Transmission—Ultrasonic Echo Divisional Reception System
FIG. 14A is a schematic diagram for explanation of an example of a state of transmitting an ultrasonic beam according to a conventional system, and similarly, FIG. 14B is a schematic diagram for explanation of an example of a state of receiving an ultrasonic beam according to a conventional system.
In this system, ultrasonic pulses are intermittently transmitted from respective plural ultrasonic transducers 101 included in an ultrasonic transducer array 100 based on drive signals that are fed from plural pulsers connected to a transmitting unit. As shown in FIG. 14A, this ultrasonic pulse is transmitted from the ultrasonic transducer array 100 toward an object to be inspected, and propagates within the object to form an ultrasonic beam 102. The ultrasonic beam 102 becomes narrower gradually as it travels in a region at a short distance from the position from which the beam is transmitted, narrowest at a focal point F, and gradually broader afterwards. This ultrasonic beam is reflected by a reflector that exists within the object, thereby an ultrasonic echo is generated, and, as shown in FIG. 14B, this ultrasonic echo is received by the ultrasonic transducer array 100. Detection signals outputted from the plural ultrasonic transducers 101 included in the ultrasonic transducer array 100 are accumulated after predetermined delays are given thereto respectively by plural phase matching computing means connected to a receiving unit, and thereby a detection signal with respect to each received ultrasonic beam is obtained. In this example, three received ultrasonic beams 103, 104, and 105 are shown.
(2) Multidirectional Ultrasonic Beam Transmission—Ultrasonic Echo Non-divisional Reception System
FIG. 15 is a schematic diagram for explanation of another example of a state of transmitting and receiving an ultrasonic beams by a conventional system.
In this system, plural kinds of drive signals are fed to the ultrasonic transducer array 100. Thereby, from plural sets of pulsers, the plural kinds of drive signals are simultaneously fed to the plural ultrasonic transducers 101 included in the ultrasonic transducer array 100. For example, as shown in FIG. 15, two sets of timing pulses of pulse set A and pulse set B are applied to one set of elements, and both ultrasonic beam A and ultrasonic beam B are generated. Note that, in the case where one pulse of the pulse set A and one pulse of the pulse set B are superposed to each other, that forms a common pulse. These ultrasonic beams A and B are transmitted toward the object simultaneously in plural directions (for example, two directions).
In the above-described ultrasonic diagnosing method and ultrasonic diagnosing apparatus, recently, it is required that the resolution is improved and real time performance is improved by performing imaging at a higher speed. On this account, R. E. Davidsen et al. “TWO-DIMENSIONAL RANDOM ARRAYS FOR REAL TIME VOLUMETRIC IMAGING”, ULTRASONIC IMAGING 16, 1994, pp. 143-163 discloses that the number of ultrasonic beams transmitted within a predetermined period is increased.
However, in the above references, the problem of crosstalk in the multi-beam transmission and reception is not considered, and conditions or means required to suppress crosstalk is not disclosed. Further, ideas for grasping an amount of crosstalk quantitatively by using a number of transmission beams or a number of receiving focal points as a parameter are not described.